Rotary planographic printing press

ABSTRACT

A rotary planographic printing press wherein a hydrophobic photoconductive recording layer carried on the printing cylinder of the press is exposed to acquire a latent photoconductive image of the information to be printed and is then developed by means of an aqueous conductive developing liquid applied to the photoconductive recording layer under an external electrical field of such a polarity as to attract such liquid differentially into wetting relation with the recording layer surface in accordance with the exposed image thereon, a hydrophobic planographic printing ink is applied to the thus selectively wetted recording layer so as to adhere selectively to the unwetted areas of the recording layer while being repelled from the wetted areas thereof, and the ink image thus obtained is printed onto a copy sheet fed to the press. Preferably the press includes an off-set cylinder operating in conjunction with an impression cylinder. Preferably, the aqueous developing liquid and the hydrophobic printing ink are applied by means of a common applicator roller onto which is applied a fine screen pattern of the ink and in the uninked open areas the aqueous developing liquid is applied.

. United States Patent Miiller [54] ROTARY PLANOGRAPHIC PRINTING PRESS [72] lnventor: Rodolf Miiller, Deisenhofen, Ger- 96/33, 101/147, 101/451, 101/465, 101/471 [51] Int. Cl. ..G03b 27/12, G03f 7/10, B41125/00 [58] Field of Search ....10l/l48; 96/1, 1 A, 1 LX, 31,

[56] References Cited UNITED STATES PATENTS 3,372,027 3/1968 Gundlach et a1. ..96/1 LX 3,152,969 10/1964 Eastman ..101/456 X 3,011,963 12/1961 Johnson et al ..101/426 X 2,622,521 12/1952 Larsen ..101/148 2,690,119 9/1954 Black ..101/148 2,733,654 2/1956 Rogers ..101/148 3,285,741 11/1966 Geisierich et a1 ...96/l R Oct. 17,1972

3,299,787 1/1967 1401b et al ..96/1 A x 3,309,990 3/1967 Klupfer et al ..101/467 FOREIGN IPATENTS'OR APPLICATIONS 267,341 5/1964 Australia ..96/1 LX Primary Examiner- Clyde l. Coughenour Attorney-William J. Daniel 57 ABSTRACT A rotary planographic printing press wherein a hydrophobic photoconductive recording layer carried on the printing cylinder of the press is exposed to acquire a latent photoconductive image of the information to be printed and is then developed by means of an aqueous conductive developing liquid applied to the photoconductive recording layer under an external electrical field of such a polarity as to attract such liquid differentially into wetting relation with the recording layer surface in accordance with the exposed image thereon, a hydrophobic planographic printing ink isapplied to the thus selectively wetted recording layer so as to adhere selectively to the unwetted areas of the recording layer. while being repelled from the wetted areas thereof, and the ink image thus obtained is printed onto a copy sheet fed to the press. Preferably the press includes an off-set cylinder operating in conjunction with an impression cylinder. Preferably, the aqueous developing liquid and the hydrophobic printing ink are applied by means of a common applicator roller onto which is applied a fine screen pattern of the ink and in the uninlred open areas the aqueous developing liquid is PATENTEDUET 11 m2 SHEEI 1 OF 2 INVENTOR RUDOLF MULLER BY WATSON, COLE, GR/NDLE 8 WATSON ATTOR N EYS PATENTED 17 I972 3.698.312

sum 2 or 2 I N VE NTOR PUDOLF MULLER BY WA TSON, COLE GR/NDLE & WATSON ATTORNEY ROTARY PLANOGRAPHIC PRINTING PRESS The present application is a continuation-inpart of the Pat. application No. 503,696 filed Oct. 23, 1965, now abandoned.

This invention relates to a planographic printing process, especially an offset printing process, wherein the non-printing areas of the printing form before inking are made ink-repellent by moistening.

For carrying out such a process a printing plate is needed the surface of which possesses an image-wise different wettability. Up to now this wettability could only be realized by mechanical operated application of non-wettable substances or by a photographic development process. These both steps at least partly had to be performed outside the printing machine, so that more time was spent for the sole bracing and removing of the printing plates than could be justified economically for the production of single or plural copies.

On the other hand, however, the electrostatic duplicating process, which is better suited for this purpose, possesses the disadvantage that larger apparatus are needed and that the quality of the prints is not suffi cient for all purposes. In these processes, moreover, the short time for producing the printing plate is opposed to the quite slow speed of printing, so that the amount of copies which can be printed economically, is very limited.

It has been proposed already to simplify and to improve the electrophotographic process by inking an image-wise exposed photoconductive member with a dyestuff, which is soluble in a dielectric liquid. The dielectric liquid wets only those areas of the photoconductive member which possess an opposite potential with respect to the surface of the supply roller as a result of the charge image or the conductivity image which has been formed by exposure. Hence, the dielectric liquid deposits the dye dissolved in it only on these areas. However, neither the speed of printing nor the quality of the prints made by a planographic printing process or an offset printing process can be achieved thereby.

According to the present invention an image-wise exposed photoconductive layer is used as a printing form and an aqueous electrically conductive liquid as wetting medium for planographic printing purposes.

According to a known electrophotographic' recording process a charge image is formed onto a photoconductive layer by uniformly charging and subsequent image-wise exposing said layer, whereupon the development is carried out by means of a conductive aqueous liquid presented to this charge image in a uniform distribution.

According to another recording process a conductivity image can be formed in a known way by imagewise exposure of a photoconductive layer and said image developed with an aqueous conductive liquid while creating an electrostatic charge pattern by applying an electrical potential difference between said liquid and the exposed photoconductive layer.

An apparatus operating according to the principles of the last mentioned recording process is only of relatively limited dimensions and the manufacture of a printing plate takes no more time than in the case of the known electrophotographic recording processes using a corona charging device. The plate can be completed within a slow revolution of the printing cylinder. The

print, however, is obtained by means of a usual printing ink of a common quality for planographic printing. Printing can occur directly from the printing roller onto the printing carrier. Preferably, however, the printing image should first be transferred onto a rubber-covered roller according to the offset-printing process, in order to prevent the sensitive photoconductive layer from coming into contact with the printing carrier. It has been found moreover that the print on the printing carrier becomes sharper by the previous transfer on a transfer roller. Of course, the image-wise exposure should occur by means of an odd number of mirrors in order to obtain the true-sided position of the image on the printing carrier.

If several copies are required, the printing plate for that reason need not be exposed again after each print, because already after the first inking'it has become moisture-repellent on the ink-carrying areas, whereas the initially wetted image areas still remain wettable. Further prints can also be produced in a known way on paper sheets bearing fatty ink marks after switching off the exposure apparatus and occasionally the potential applied between printing roller and wetting roller and at a rate, which is usual for these sheets. After achieving the desired number of copies, the printing form remaining in the machine needs but cleaning, e.g., by an automatic cleaning device, in order to make the printing roller apt to receive another printing image.

The wetting medium is supplied by means of a wetting device comprising a liquid trough, a dipping roller and an application roller for said wetting medium. Preferably, this wetting device is isolated from the machine body. A very simple machine construction is realized when the wetting medium is presented by a combined inking and wetting device, wherein said wetting medium reaches the printing plate in a way known by itself in the form of a skin covering the ink layer. According to a further embodiment of this invention, an application roller for the wetting medium may be used, which is provided with a fine screen made of a moisture'repelling substance. E.g., the application roller can be printed with a fine screen of printing ink, which screen is continuously supplied with ink taken from a reservoir.

According to a further characteristic of this invention, as photoconductive layer a zinc oxide sheet is used, which can be braced onto the printing roller. With regard to their moisture and ink-taking, these sheets possess favorable properties and can readily be replaced when they are used up after a considerable time of operation. The printing image, which has been produced on such a sheet after the first inking step, occasionally can also be stored outside the machine or can be duplicated on a usual planographic printing machine.

The device according to this invention comprises l. a printing roller provided with a photoconductive surface,

2. at least one aqueous electrically conductive developing liquid applicator roller, which is insulated electrically with respect to this printing roller and which possesses an electrical tension i.e., voltage different from that of the printing roller surface,

3. at least one ink applicator roller, and

4. an exposure device for exposing the original to be reproduced by printing.

In order to obtain positive prints from positive originals the applicator roller for the aqueous electrically conductive developing liquid should have an electrical potential that is positive with respect to that of the printing roller, so that the aqueous electrically conductive liquid selectively wets the hydrophobic photoconductive zinc oxide sheet in the unexposed and uncharged areas.

In order to obtain negative prints from positive originals the applicator roller for the aqueous electrically conductive developing liquid should have an electrical potential that is negative with respect to that of the printing roller, so that the aqueous electrically conductive liquid selectively wets the photoconductive zinc oxide in the exposed areas.

According to a preferred embodiment of this invention, the moisture applicator roller constitutes the main part of a wetting device, which is insulated against the machine body and which has been assembled as a combined inking and wetting device, wherein the wetting medium is transferred in a known way in the form of a skin overlying the ink.

An especially favorable method of application can be realized in such an inking device, when the applicator roller of liquid is provided with a fine screen of nonwettable substances. Particularly, the applicator roller of liquid can cooperate with the inking roller, which transfers the printing ink in the form of a fine screen onto the former.

According to a further characteristic of the invention a copying system is provided preferably working on an image scale of 1:1 as well as a transport slide for the printing original, which transport slide can be drivingly connected with the printing roller in such a way, that it is moved at a speed corresponding with the image scale in a direction opposite to that of the surface of the printing roller, so that no relative motion takes place between the reproduction of the moving original and the surface of the printing roller that would impair the definition of the reproduction.

According to a further embodiment of the present invention, the printing roller may cooperate with a known rubber-covered roller. Moreover, an automatic cleaning device known by itself can be provided for the printing roller and the rubber-covered roller.

Finally, in order to turn to profit the printing speed attainable by the process according to this invention, the printing machine can be equipped with an automatic conveyor mechanism for paper.

Some embodiments are illustrated in the following drawings.

FIG. 1 is a schematic representation of a printing machine according to this invention.

FIG. 2 is a combined inking and wetting mechanism.

In FIG. 1 the numeral 1 designates a printing cylinder onto which a zinc oxide sheet has been attached by means of a clamping device 3. This clamping device is not shown in detail in the drawings. It may be a known type of clamping device commonly in use for attaching flexible printing sheets.

In a manner also known in offset printing machines the printing cylinder 1 cooperates with a rubber covered cylinder 4 and a back pressure cylinder 5. On the rubber covered cylinder 4 a rubber cloth 7 has been clamped by means of the clamping device 6. The back pressure, i.e., impression cylinder comprises a gripper 8, which is closed by a tension spring 9 and which is opened by the displacement of its nose shaped element 8a by means of the cams of a cam disk 10.

On a table 11 lies a stack 12 of paper copy sheets the uppermost sheet of which is fed each time to' the machine by a feeder element 14. The driving of the feeder element 14 is performed by a disk 15 fitted on the shaft 5a of the back pressure cylinder 5 over the guide rod 17 bearing the diagrammatically illustrated slide member 16. The cam disk 10 is arranged in a known way so as to permit the gripper 8 to grip at the right moment the paper sheet 13 which is conveyed into the machine between the back pressure cylinder 5 and the rubber covered cylinder 4 and which is removed by a scraper 18 guiding the sheet to the stacking table 19.

The printing cylinder 1 is further in contacting relationship with an applicator roller 20 of a usual inking fountain device. In the present case this device comprises, besides the said applicator roller 20, a distributor roller 21, a pivotable roller 22 and a ductor roller 24, which cooperates with an adjustable inking blade 23. The printing machine is further provided with an aqueous developing liquid applicator roller 25 lying in contacting relationship with the printing cylinder 1 and the clip roller 27 which rotates in a coating pan 26 and cooperates with said coating roller 25. Both rollers are journalled in the frame 28 to which the coating pan 26 is equally attached. The frame 28 is suspended on the insulating rods 29 and 30 in the machine frame (not illustrated in the drawings). The frame 28 is connected with the negative pole of a current source 31, the positive pole of which is connected to the shaft 10 of the printing cylinder 1 over a sliding contact spring 32.

The numeral 33 indicates an optical lens system by means of which an original 36 lying on a glass plate 34 of a carriage 35 is reproduced on the zinc oxide sheet 2 through the interpositioned reversing mirror 37.

To the carriage 35 a toothed rack 38 is attached, which meshes with a toothed wheel 39 being itself capable of engaging by axial displacement a toothed wheel 40 which is connected in fixed relationship to the printing cylinder 1 so as to bodily move therewith. The pitch circle of the toothed wheel 40 coincides with the surface of the zinc oxide sheet 2, so that the linear speed of the carriage 35 is equal to the linear speed of the zinc oxide sheet 2 (=the peripheral speed of the toothed wheel 40 or printing cylinder 1). In reproducing the part of the original 36, passing behind a stationary slit 41, on the zinc oxide sheet 2, no relative motion between the reproduction and the sheet surface occurs so far as the optics 33 provides for a reproduction scale of 1:1.

The exposure of the original 36 is done by two preferably tubular light sources 43 and 44 which are positioned at either side of the slit in a protective housing 42.

Finally the printing machine comprises two cleaning devices, one for the printing cylinder 1 and the other for the rubber covered cylinder 4, which are journalled on a shaft 45 (45a) solidly attached to the machine frame. Each of the cleaning devices consists of an angle forming lever 47 (47a) provided with a handle 46 (46a), said lever 47 (47a) bearing a cleaning roller 48 (48a) which dips into a solvent containing pan 49 (49a). In inoperative position the lever 47(47a) rests against a stop member 50 (50a), solidly mounted on the machine frame, under the influence 'of the weight of the handle 46 (46a), so that the cleaning roller 48 (48a) is not in contacting relationship with the printing cylinder 1 or with the rubber covered cylinder 4. For cleaning one of both cylinders the handle 46 (46a) is taken and lifted up. Upon rotation of said two cylinders the corresponding cleaning roller 48 (48a) is urged to the corresponding cylinder by means of the handle 46 (46a). During this action the applicator roller must, of course, be directed away from the printing cylinder 1. It is obvious to use any other known automatic cleaning device instead of the illustrated cleaning device.

The operation of the complete machine is as follows.

The original to be printed is put on the carriage 35 which has previously been coupled to the printing cylinder 1 over the toothed wheels 39, 40. By a movement of the carriage from the left to the right or reversed, which movement corresponds to one complete revolution of the printing cylinder 1 and during which movement the lamps 43 and 44 are switched on, the original 36 is reproduced on the peripheral surface of the cylinder 1 or on the surface of the zinc oxide sheet 2. This sheet must, of course, be protected against the penetration of undesirable light. By imagewise exposing the surface of the zinc oxide sheet differences in conductivity, are formed in said sheet.

Upon rotation of the cylinder 1 in the direction indicated by the arrow, the areas of the zinc oxide sheet exposed at the exposure station, which have become image-wise differentially conductive, reach the developing liquid roller 25. Due to the action of the applied voltage source 31 the exposed areas of the zinc oxide sheet, which were rendered conductive take an opposite potential withrespect to the developing liquid applied with the applicator roller 25, so that in case the developing liquid is connected to the positive pole of the source 31 the zinc oxide sheet is wetted in the unex posed areas and in case the developing liquid is connected to the negative pole of the source 31 the zinc oxide sheet is wetted in the exposed areas. Continuing the rotation of the cylinder 1 in the direction indicated by the arrow, the now image-wise moistened areas of the layer reach the inking roller 20, whereby only the non-moistened areas can take up ink. In this way image-wise inking of the exposed areas of sheet 2 takes place.

After a complete revolution of the printing cylinder 1 its driving connection with the carriage 35 may be interrupted so that the carriage is stopped. After about 1% revolutions the inking is completed and after about 2 revolutions the full transfer of the inked image to the rubber cloth 7 has finished. The image produced on this cloth can arbitrarily be printed while the imagewise moistening and inking is continued. The exposure unit need no more be operative since during the first inking the printing areas have accepted enough ink to make these areas moisture-repellent, whereas the non printing areas continue to accept moisture and remain thereby ink-repellent.

As soon as the desired number of prints has been prepared, the printing cylinder 1 and the back pressure cylinder are cleaned with the help of the cleaning rollers 48 (480) so that they become available for the preparation of a print from another original. By means of the described machine a print from an original can be prepared in a shorter time than was otherwise possible.

FIG. 2 illustrates a moistening roller 52 which dips into a wetting liquid containing pan 51 and which cooperates with a wetting liquid coating roller 53 lying against a coating roller 54 which is provided with a graved or etched screen. The numeral 55 indicates a uniformly rotating ink ductor roller, which together with an adjustable blade 56 forms an ink storage space 57. Upon rotating in the direction of the arrow the ink ductor roller 55 takes up an ink film from the ink storage space 57, the thickness of said film being controlled by means of a blade adjusting screw 59. The inking roller 54 will only be moistened by the ink film at its heightened screen portions 54b and in consequence thereof the ink film is transferred in the form of this screen to the surface of the wetting liquid coating roller 53. For the same reason as set forth above the film of water 60 taken up by the moistening roller 52 can only pass therefrom to these areas of the coating roller 53 which are not covered with ink. A screen formed of small ink spots and small droplets of water lying therebetween is produced in these areas. As explained hereinbefore these droplets only pass to the developed, i.e., already wetted areas of the zinc oxide sheet 2.

The transfer of the said small water droplets from the screen surface to the printing form is helped by means of the potential difference applied between the moistening roller and the roller carrying the printing form. An external potential source 31 is applied therefor as illustrated in FIG. 2.

Iclaim l. A rotary planographic printing press comprising a printing cylinder carrying on at least a portion of its peripheral surface a hydrophobic photoconductive recording layer; means for rotating said cylinder, means operative at one locus on the cylinder periphery to image-wise expose said photoconductive layer to produce a latent conductivity image in said layer; means operative at a subsequent locus on said periphery to develop said latent image, said developing means including means for delivering an aqueous conductive developing liquid to said photoconductive layer generally uniformly thereover, said. aqueous developing liquid being normally repelled by said hydrophobic layer, and means for creating an applied external electrical field passing through said layer comprising an external voltage source having one pole electrically connected to said conducting liquid and the other pole connected to an electrode behind said layer, as to create in said layer an electrostatic charge pattern of polarity opposite to the polarity of the developing liquid and of such intensity as to attract said liquid into wetting relation with the areas of said layer carrying said charge pattern while the remaining areas repel said liquid; means for applying a hydrophobic planographic printing ink to said selectively wetted developed recording layer, said ink being repelled from the wetted areas thereof and adhering to the unwetted areas thereof to give a hydrophobic ink image; and means for feeding a copy sheet to said press to receive said ink image, said developing liquid and printing ink delivery means being comprised by a single applicator roller together with means for applying a fine screen pattern of ink to the surface of said roller and means for applying developing liquid to the uninked open areas of said screen pattern.

2. The printing press of claim 1 including an offset cylinder and an impression cylinder rotating in synchronism with said printing cylinder, said ink image being transferred from said printing cylinder to said offset cylinder, said copy sheet feeding means feeding said sheet between said offset and impression cylinders.

3. The printing press of claim 1 wherein said developing liquid delivering means comprises an. electrically conductive moistening roller having its surface tern and means for contacting said ink applicator roller with ink.

5. The printing press of claim 1, wherein said means for applying said ink pattern comprises a fine screen pattern of hydrophobic material on said single roller and means for contacting said roller surface with developing liquid and ink in succession, said ink selectively adhering to said material pattern and said liquid selectively adhering to the areas of said roller uncovered by said pattern.

6. The press of claim 1, wherein said exposing means comprises feeding means for delivering an original to be printed at a speed in synchronism with the peripheral speed of said printing cylinder, means for illuminating said original and optical means for reflecting an image to said original upon said recording layer.

7. The press of claim 1 comprising means at a further locus on said printing cylinder periphery operative to remove the developing liquid from the areas of the cylinder surface wet thereby, whereby said recording layer can be reused for additional exposures. 

1. A rotary planographic printing press comprising a printing cylinder carrying on at least a portion of its peripheral surface a hydrophobic photoconductive recording layer; means for rotating said cylinder, means operative at one locus on the cylinder periphery to image-wise expose said photoconductive layer to produce a latent conductivity image in said layer; means operative at a subsequent locus on said periphery to develop said latent image, said developing means including means for delivering an aqueous conductive developing liquid to said photoconductive layer generally uniformly thereover, said aqueous developing liquid being normally repelled by said hydrophobic layer, and means for creating an applied external electrical field passing through said layer comprising an external voltage source having one pole electrically connected to said conducting liquid and the other pole connected to an electrode behind said layer, as to create in said layer an electrostatic charge pattern of polarity opposite to the polarity of the developing liquid and of such intensity as to attract said liquid into wetting relation with the areas of said layer carrying said charge pattern while the remaining areas repel said liquid; means for applying a hydrophobic planographic printing ink to said selectively wetted developed recording layer, said ink being repelled from the wetted areas thereof and adhering to the unwetted areas thereof to give a hydrophobic ink image; and means for feeding a copy sheet to said press to receive said ink image, said developing liquid and printing ink delivery means being comprised by a single applicator roller together with means for applying a fine screen pattern of ink to the surface of said roller and means for applying developing liquid to the uninked open areas of said screen pattern.
 2. The printing press of claim 1 including an offset cylinder and an impression cylinder rotating in synchronism with said printing cylinder, said ink image being transferred from said printing cylinder to said offset cylinder, said copy sheet feeding means feeding said sheet between said offset and impression cylinders.
 3. The printing press of claim 1 wherein said developing liquid delivering means comprises an electrically conductive moistening roller having its surface in substantial rolling contact with said impression cylinder surface, and means for applying said liquid to said roller surface, said moistening roller being connected to said first pole of said voltage source and being mounted in insulated relation from the remainder of the press.
 4. The printing press of claim 1, wherein said means for applying said ink pattern comprises an ink applicator roller having on its surface a raised fine screen pattern and means for contacting said ink applicator roller with ink.
 5. The printing press of claim 1, wherein said means for applying said ink pattern comprises a fine screen pattern of hydrophobic material on said single roller and means for contacting said roller surface with developing liquid and ink in succession, said ink selectively adhering to said material pattern and said liquid selectively adhering to the areas of said roller uncovered by saId pattern.
 6. The press of claim 1, wherein said exposing means comprises feeding means for delivering an original to be printed at a speed in synchronism with the peripheral speed of said printing cylinder, means for illuminating said original and optical means for reflecting an image to said original upon said recording layer.
 7. The press of claim 1 comprising means at a further locus on said printing cylinder periphery operative to remove the developing liquid from the areas of the cylinder surface wet thereby, whereby said recording layer can be reused for additional exposures. 